The present invention relates to an apparatus for cooling molten metal in a mold, and more particularly to the apparatus which cools the molten metal in the mold through cooling means provided in a casting cavity.
It is known that it is preferable to expedite the solidification of the molten metal in the mold and perform directional solidification in order to manufacture a cavity-free aluminum alloy.
Heretofore, in gravity die casting and the low pressure die casting, molten metal was solidified in dies cooled by water or air. However, strict temperature control of the die is required so that potential supercooling of the die can be obviated. The temperature of the die is periodically varied with the manufacturing cycle. Therefore, a high level temperature control is needed. In order to attain this, a complicated die structure was needed and the manufacturing cost increased because a cooling system was installed within the die.
Moreover, the positions, forms and volumes of the molten metal riser were experimentally determined to create directional solidification to obviate problems associated with the occurrence of a shrinkage cavity or vug in the die casted piece. However, the positions, forms and volumes of the riser were restricted by the shape and form of the die. Therefore, it is often impossible to create directional solidification by only modifying the riser.
Another widely practiced technique is placing a coating of a refractory material on the metal die. The die is designed to control the solidification rate of the molten metal therein by selectively choosing the refractory composition and the coating thickness of the refractory lining. This technique has difficulties associated with accurately controlling the solidification rate of the molten metal because of the heat transfer mechanism which occurs between the molten metal, the refractory coating layer and the die.